The structure of tricyclo[3.3.2.0]decane (hexahydrobullvalene) – A gas-phase electron diffraction (GED) study

The molecular structure of tricyclo[3.3.2.0^2.8]decane (hexahydrobullvalene) has been determined experimentally by gas-phase electron diffraction as well as by quantum chemical calculations. The bond lengths (twofold standard deviations in parentheses) in the skeleton [1.496(7) in the cyclopropane ring, 1.527(10) adjacent to it, 1.550(22) for the central bonds in the bridges and 1.548(16) Å for the bonds originating from the singular bridgehead] all can be explained in terms of the features of this cage hydrocarbon. All three CCC valence angles [113.0(8)° at the singular bridgehead, 112.8(12) adjacent to it and 122.3(20) adjacent to the skeletal cyclopropane ring] are larger than the regular tetrahedral angle on an sp³-hybridized carbon atom. The two-carbon bridges between the skeletal cyclopropane ring and the opposite bridgehead are twisted with a dihedral angle of 43(2)°, i.e. significantly less than the approximately 60° in n-butane in its synclinal (gauche) conformation.     

Na12Ge17: A Compound with the Zintl Anions [Ge4]4— and [Ge9]4— — Synthesis,Crystal Structure,and Raman Spectrum

Na₁₂Ge₁₇ is prepared from the elements at 1025 K in sealed niobium ampoules. The crystal structure reinvestigation reveals a doubling of the unit cell (space group:P2₁/c; a = 22.117(3)Å, b = 12.803(3)Å, c = 41.557(6)Å, β = 91.31(2)°, Z = 16; Pearson code: mP464), furthermore, weak superstructure reflections indicate an even larger C‐centred monoclinic cell. The characteristic structural units are the isolated cluster anions [Ge₉]^4— and [Ge₄]^4— in ratio 1:2, respectively. The crystal structure represents a hierarchical cluster replacement structure of the hexagonal Laves phase MgZn₂ in which the Mg and Zn atoms are replaced by the Ge₉ and Ge₄ units, respectively. The Raman spectrum of Na₁₂Ge₁₇ exhibits the characteristic breathing modes of the constituent cluster anions at ν = 274 cm^—1 ([Ge₉]^4—) and ν = 222 cm^—1 ([Ge₄]^4—) which may be used for identification of these clusters in solid phases and in solutions. Raman spectra further prove that Na₁₂Ge₁₇ is partial soluble both in ethylenediamine and liquid ammonia. The solution and the solid extract contain solely [Ge₉]^4—. The remaining insoluble residue is Na₄Ge₄. By heating the solvate Na₄Ge₉(NH₃)_n releases NH₃ and decomposes irreversibly at 742 K, yielding Na₁₂Ge₁₇ and Ge.     

Synthesis of dicyclopenta[a,e]pentalenes via a molybdenum carbonyl mediated tandem allenic Pauson-Khand reaction and the X-ray crystal structure of a planar dicyclopenta[a,e]pentalene

Two 14 pi cross-linked annulenes which belong to the family of dicyclopenta[a,e]pentalenes have been synthesized, 14 pi bis enol triflate ester 27 and the 3,7-diisopropylsilyl substituted 14 pi dicyclopenta[a,e]pentalene 30. The new allenic tandem Pauson-Khand reaction mediated by Mo(CO)(6) was employed as the key process to construct the core of the tetracycles. The two linear dicyclopenta[a,e]pentalenes 27 and 30 underwent significant electronic delocalization, perhaps even aromaticity, as revealed by the X-ray structure of 27. The tetracyclic rings in 27 assumed a flat geometry (Figure 4); the bond lengths of the tetracycle in 27 also fit well into the criteria for aromatic compounds. A comparison of the NMR and UV spectra of both 27 and 30 demonstrated that they both exhibited similar electronic properties, therefore, the purple colored 14 pi cross linked annulene 30 is planar as well as delocalized.     

Bredt's rule. IV—the structure of an alleged bicyclo[3.3.1]nonan-2-ol-9-one

Claims that the condensation product of (?)-menthone with benzylideneacetophenone is a bridged bicyclic ketol are shown to be erroneous. The true structure is shown by ¹³C n.m.r. to be 2-(1′,3′-diphenyl-3′-oxopropyl)-3-methyl-6-isopropylcyclohexanone.     

A new approach to the synthesis of benzofuro[3,2‐b]quinolines,benzothieno[3,2‐b]quinolines and indolo[3,2‐b]quinolines

Treatment of 2‐hydroxy‐, 2‐mercapto‐, and 2‐ethoxycarbonylamino‐benzonitriles 12 with 2‐fluoro‐ or 2‐nitrophenacylbromides 13 under alkaline conditions provided the corresponding benzofuran, benzothiophene, and indole intermediates 10 , respectivelly. Nucleophilic cyclization of these compounds led to the corresponding tetracyclic quinolinones 7a, 7b , and 3. Denitrocyclization reaction of compounds 10 (R = NO₂) was found especially useful. Compounds 7a, 7b , and 3 were converted to their chloro derivatives 14a‐c , which were reduced with hydrogen and a catalyst to the corresponding compounds 8a, 8b , and 2. The presented pathway represents a new method of preparation of quindoline 2 and its O and S analogs 8. Chloro derivatives 14 are reactive enough to provide the corresponding methoxy derivatives 15 and dimethylamino derivatives 16. Methylation of compounds 7a and 7b with iodomethane providing mixtures of major N‐methyl derivatives 17 and minor O‐methyl derivatives 15 were also studied.     

Studies of cyclic acetals. XXII—limitations on the use of alkyl substituents as pseudoisotopic labels: The electron impact mass spectra of alkylated derivatives of 3,7,9- and 4,7,9-trioxabicyclo[4·2·1]nonanes

Low resolution, electron impact mass spectra are tabulated for eleven methylated derivatives of 3,7,9-trioxabicyclo[4·2·1]nonane, 4,7,9-trioxabicyclo[4·2·1]nonane and nine methylated derivatives, and 6-ethyl-3,7,9-trioxabicyclo[4·2·1]nonane. In general, a substantial proportion of the fragmentation subsequent to electron impact can be rationalized according to a few, simple decomposition pathways that are inferred from analysis of mass number shifts caused by changes in substitution; however, major alterations in fragmentation are apparent in a few of these examples, which signals that, for several of the 4,7,9-trioxabicyclo[4·2·1]nonanes, the substituent acts not as an inert label but as a fragmentation-directing group.     

Reactions of the Complexes ReNCl2(PMe2Ph)3, [ReNCl4]—, [OsO3N]—, and Cl3VNCl with Metal Halides

The nitrido complexes ReNCl₂(PMe₂Ph)₃ and [OsO₃N]^— have strong basic terminal nitrido ligands which can react with Lewis acidic metal halides to form nitrido bridges. The synthesis and structure of complexes with ReNCl₂(PMe₂Ph)₃ and nitrido bridges Re≡N‐M (M = B, Ga, Sn, Ti, Zr, V, Nb, Ta, Mo, Re, Pd, Au, and Zn) as well as of complexes with [OsO₃N]^— and nitrido bridges Os≡N‐M (M = Pd and Pt) are reported. Strong Lewis acids can also remove phosphine or chloro ligands from ReNCl₂(PMe₂Ph)₃. The resulting complex fragments subsequently combine to yield oligomeric complexes with nitrido bridges Re≡N‐Re. If the reaction with strong Lewis acids is carried out in a chlorinated solvent the solvent can be decomposed to form HCl which then protonates the nitrido ligand affording an imido complex. [ReNCl₄]^— is able to form nitrido bridges to electrophilic halides if a donor ligand is coordinated in trans position to the nitrido ligand to enhance its basicity sufficiently. The synthesis and structure of examples with nitrido bridges Re≡N‐M (M = Pd, Pt, Ta) are reported. The chloro imido complex Cl₃V≡N‐Cl can act as a nitride ion transfer reagent. Its reaction with MoCl₅ yields Mo₂NCl₈ whereas with MoCl₃ the nitride chlorides Mo₃N₂Cl₁₁ and MoNCl₃ are obtained. Cl₃VNCl can also act as an reactive intermediate by the reaction of VN with a halide as was shown by the reaction of MoCl₅ with VN yielding Mo₂NCl₇. The structures of these molybdenum nitride chlorides are discussed.     

Effects of electron correlation and spin projection on rotational barriers of trithiocarbenium ion [C(SH)3]+ and Radical Dication [C(SH)3]⋅,2+

Theoretical level dependencies are discussed of relative isomer stabilities and rotational barriers of trithiomethyl cation [C(SH)₃]⁺ ( a ) and of radical dication [C(SH₃)]^⋅,2+ ( b ). Spin polarization and dynamic electron correlation are very important for the radical dictation. Removal of an electron from one of the degenerate π-HOMOs of C_3h symmetric [C(SH)₃]⁺ stabilizes the remaining π electron to such an extent that the unpaired electron is not in the HOMO of the dictation. The radial π MO's “diving below the Fermi level” facilitates strong spin polarization because of its energetic proximity to σ MOs. Projection of the first three higher spin states eliminates spin contaminations, and the terms E(PUHF(s+3))-E(UHF) and E(PMP4(s+3))-E(MP4) are discussed. The combination of annihilation of spin contamination and electron correlation is essential for the determination of relative energies and rotational barriers of the radical dication. The results obtained at this level match the results of high level QCISD(T) calculations in a near-quantitative fashion. Perturbation theory alone does not correct for spin contamination even if it is carried to full fourth order and includes triple excitations; the E(PMP4(s+3))-E(MP4) values are all negative and can exceed 5 kcal/mol in magnitude. Previous studies showed that annihilation of spin contaminations is important in regions of potential energy surfaces where σ bonds are broken (homolytic dissociation), formed (radical addition), or both (H abstraction by radical). Our findings stress that the annihilation of spin contaminations can be just as important for any process that greatly alters spin polarization and even if that process proceeds without breaking or forming of σ bonds. For comparison, density functional theory also was employed in the potential energy surface analyses. The results obtained with the B3LYP formalism were found to be less susceptible to spin contamination and resulted in rather good agreement with the best pertubation and configuration interaction results. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 :1023–1035, 1997     

An alternative approach to the synthesis of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles,their crystal structure,and DFT calculations

New representatives of [1,2,4]triazolo[1,5-a]pyridine-8-carbonitriles were synthesized via the condensation of β-diketones or β-dialdehydes and characterized using MS spectrometry, ¹H, ¹³C and, ¹⁹F NMR and IR spectroscopy. Crystal structures of two compounds were established using X-ray analysis and showed that title compounds are prone to the formation of planar molecules. The absence of band responsible for CN stretching vibration in trifluoromethyl-containing compounds was explained using the DFT calculations method, which also showed a significant influence of fluorines introducing on the energy gap between HOMO and LUMO.     

Theoretical study of the photochemical [2 + 2]-cycloadditions of cyclic and acyclic alpha,beta-unsaturated carbonyl compounds to ethylene

The ground and first triplet excited-state potential energy surfaces of the [2 + 2]-cycloadditions of 2-cyclohexenone, methyl acrylate, and methyl crotonate to ethylene have been studied by means of CASSCF and DFT-B3LYP calculations. The attack of ethylene to the (3)(pi-pi) alpha,beta-unsaturated carbonyl compound leads to the formation of a triplet 1,4-biradical intermediate that evolves to the ground-state potential energy surface. The outcome of the reaction is governed by the competition between the deactivation of the (3)(pi-pi) alpha,beta-unsaturated carbonyl compound itself and its reaction with ethylene to form the triplet 1,4-biradical. For 2-cyclohexenone, the potential energy barrier corresponding to the formation of the biradical intermediate is lower than for the acyclic systems. On the other hand, the energy necessary to reach the crossing point between the (3)(pi-pi) and the ground-state potential energy surfaces is lower for the acyclic systems than for 2-cyclohexenone. For methyl acrylate and methyl crotonate, the decay of the (3)(pi-pi) state of the isolated molecule is therefore expected to be faster than the formation of the 1,4-biradical, so that the [2 + 2]-cycloaddition will not take place. However, for 2-cyclohexenone the formation of the triplet 1,4-biradical is favorable, and the process will lead to the formation of the corresponding cyclobutane derivative.     

Selectivity in cycloadditions—VII: Cycloadditions of nitrile oxides to thiophene and benzo[b]thlophene, regiochemistry

Thiophene adds benzo- and mesitonitrile oxide yielding mainly cycloadducts 1 or products derived from them. With benzothiophene the regioselectivity of the cycloadditions of the two nitrile oxides is lower and both the cycloadducts 10 and 11 could be isolated in a 78:22 and 26:74 ratio, respectively.

Frontier orbital considerations, using EH and MINDO/3 calculations, and a comparison with the regioselectivities of related systems allowed elucidation of the observed regiochemistry. Some differences in orientation between cycloadditions and electrophilic substitution reactions of benzothiophene are pointed out and discussed.     

Synthesis of ruthenium complexes with carbonyl and polypyridyl ligands derived from dipyrido[3,2‐a:2′,3′‐c]phenazine: application to the water gas shift reaction

The preparation and spectroscopic properties of new dipyrido[3,2‐a:2′,3′‐c]phenazine ruthenium complexes are described. The complexes show high catalytic activity in the water gas shift reaction in a basic medium under mild conditions (P_CO = 0.9 atm at 100 °C). Copyright © 2002 John Wiley & Sons, Ltd.     

The application of intramolecular saturation transfer NMR spectroscopy to conformational analysis. The effect of methyl substituents on the barrier height and conformational isomer population of the tricyclo[9.3.1.03,8]pentadecane ring system.

Intramolecular saturation transfer NMR spectroscopy has been used to establish the conformational equilibria of several tricyclo[9.3.1.0^3,8] pentadecanes.